diff --git a/src/servers/sidecar/music/index.ts b/src/servers/sidecar/music/index.ts
index 7342b3fa..8454c358 100644
--- a/src/servers/sidecar/music/index.ts
+++ b/src/servers/sidecar/music/index.ts
@@ -7,6 +7,7 @@ import { startNightlyReindex, stopNightlyReindex } from './nightly-reindex';
 import { startMusicWatcher, stopMusicWatcher } from './watcher';
 import {
   reindexNow,
+  reindexFull,
   ensureCacheSetup,
   MUSIC_ROOT,
   getIndexStatus,
@@ -49,7 +50,9 @@ const DATA_PATH = process.env.DATA_PATH ?? join(process.cwd(), 'data');
 //                                          "<Type>" } }, Type ∈ Studio/Live/Compilation/Single/EP/…
 //                                          ETag: <v>; If-None-Match → 304. Source: each artist folder's
 //                                          _discography.md (normalized; the md itself is never modified).
-//   POST /reindex                          run the build to COMPLETION, then return the final IndexStatus.
+//   POST /reindex[?full=1]                 run the build to COMPLETION, then return the final IndexStatus.
+//                                          default = incremental (skips unchanged); ?full=1 = full staged
+//                                          rebuild + atomic swap (backfill a meta-format change).
 //   GET  /reindex/status                   IndexStatus snapshot.
 //   GET  /reindex/stream                   SSE. Triggers a build if idle (`?trigger=0` = watch-only).
 //                                          `event: progress` (IndexStatus) throttled ~200ms, then one
@@ -112,10 +115,13 @@ const server = Bun.serve({
     // ── Index build ──
     if (url.pathname === '/reindex') {
       if (req.method !== 'POST') return new Response('Method not allowed', { status: 405 });
-      // Run the resync to completion, THEN respond — so the caller's manifest read right after is fresh.
-      // Incremental builds are near-instant (unchanged albums skip by version stamp). reindexNow joins
-      // an in-flight build rather than starting a second.
-      const result = await reindexNow();
+      // Run to completion, THEN respond — so the caller's manifest read right after is fresh. Both join an
+      // in-flight build rather than starting a second.
+      //   default : incremental — near-instant, skips unchanged albums by version stamp.
+      //   ?full=1 : full from-scratch rebuild into a fresh slot, swapped in atomically (staged + safe) —
+      //             use to backfill a meta-format change (e.g. a new track field) across the WHOLE library.
+      const full = url.searchParams.get('full') === '1' || url.searchParams.get('full') === 'true';
+      const result = await (full ? reindexFull() : reindexNow());
       return json(result);
     }
     if (url.pathname === '/reindex/status') return json(getIndexStatus());